Never disagree with the narcissist or contradict him
Never offer him any intimacy
Look awed by whatever attribute matters to him (for instance: by his professional achievements or by his good looks, or by his success with women and so on)
Never remind him of life out there and if you do, connect it somehow to his sense of grandiosity
Do not make any comment, which might directly or indirectly impinge on his self-image, omnipotence, judgment, omniscience, skills, capabilities, professional record, or even omnipresence. Bad sentences start with: "I think you overlooked ... made a mistake here ... you don't know ... do you know ... you were not here yesterday so ... you cannot ... you should ... (perceived as rude imposition, narcissists react very badly to restrictions placed on their freedom) ... I (never mention the fact that you are a separate, independent entity, narcissists regard others as extensions of their selves, their internalization processes were screwed up and they did not differentiate properly) ..." You get the gist of it.